Personal computers and cellular phones have been rapidly spreading, and the printed-wiring boards for these devices are required to be more dense. Under these circumstances, printed-wiring boards and metal-clad laminates are required to be more reliable. Properties particularly required to be improved include heat resistance, low moisture-absorptivity and low stress which directly affect their resistance to reflow, and low thermal expansion which directly affects the connection reliability between their layers and between them and others with which they are assembled.
So far, inorganic materials have been used to realize excellent heat resistance, low moisture-absorptivity and low thermal expansion, and methods of developing composites of organic and inorganic materials have been studied to bring out the advantages of each material. One of these methods uses surface treatment agents, e.g., a silane coupling agent. A silane coupling agent has a structure with an organic functional group bonded to a hydrolyzable alkoxy group. It is known that the agent of such structure works to enhance adhesion between an inorganic material and an organic polymer, because the alkoxy group reacts with an inorganic material surface and an organic functional group with an organic polymer to bond the inorganic and organic components to each other.
Each industrial area has been utilizing and applying characteristics of enhancing adhesion between an inorganic and organic materials, and studying to further improve adhesion between these materials at their interface. For example, Japanese Patent Laid-open Publication No. 63-230729 and Japanese Patent Publication No. 62-40368 disclose methods of improving adhesion between an inorganic and organic material at their interface, where types and number of the organic functional groups which a common silane coupling agent includes are controlled in order to enhance its reactivity with an organic polymer. However, merely enhancing reactivity with an organic polymer only gives a rigid layer, and cannot be expected to notably improve adhesion, because of the difficulty in reducing residual stress or the like produced in the interface.
One of the methods for improving adhesion and also decreasing residual stress in the interface uses a long-chain polysiloxane for reducing stress in combination with a surface treatment agent (Japanese Patent Laid-open Publication Nos. 3-62845 and 3-287869). It is however very difficult for such an approach to obtain high adhesion in the interface for several reasons, e.g., very low reactivity between a surface treatment agent and long-chain polysiloxane under common treatment conditions, a common long-chain polysiloxane lacking an alkoxy group reactive with an inorganic material, and adverse effect by hydrophobicity of a methyl group or the like in a long-chain polysiloxane.
On the other hand, Japanese Patent Laid-open Publication No. 1-204953 discloses a method which uses a chain-structured polysiloxane having both an alkoxyl group and an organic functional group, the former being reactive with an inorganic material and the latter with an organic polymer. However, the polysiloxane chain in such a compound, when sufficiently long, would lie across the inorganic material surface, due to the orientation of the hydrophobic group, e.g., methyl, and does not easily enter the resin. Moreover, it will be physically adsorbed by the inorganic material in places, tending to form a rigid layer. Therefore, it is very difficult for such a compound to realize the reduced stress in the interface to the extent expected from its chain length.
A long-chain polysiloxane tends to be physically adsorbed to form a large cyclic structure, which can possibly deteriorate the properties of the organic polymer after it has been set. It is known that the above problems are effectively solved in a prepreg comprising a base of glass or the like by use, as a dispersant or base surface treatment agent, of a silicone polymer three-dimensionally condensed beforehand to have at least one functional group reactive with a hydroxyl group on the inorganic material surface and at least one organic functional group reactive with the organic polymer (Japanese Patent Laid-open Publication Nos. 10-121363, 11-60951 and 11-106530).
Under these circumstances, novel materials, such as a resin composition formable into a film and having by itself excellent properties of low stress and low thermal expansion irrespective of the base material on which it is placed, and a resin film of such a composition, have been demanded to correspond to requirements for wiring of higher density for semiconductor-carrying bases.